Historically, shotguns were the well known single and double barrel embodiments utilizing manually loaded and ejected ammunition. Progressively, a variety of fixed and detachable methods to hold and feed ammunition into the firing chamber have been used.
AR10 and AR15 “AR rifles” date back to 1955 and 1958, respectively.
AR rifles feature ergonomic controls, parts commonality, and operational functionality that are integrated across all “AR” models making the AR rifles well suited to sporting and tactical applications.
AR rifles are comprised of three principle modular component sub-assemblies which can be readily disassembled without tools.
The AR rifle sub-assemblies include: the upper receiver, which includes the cartridge loading mechanism, firing chamber, barrel and spent cartridge ejection mechanism; the lower receiver, which includes the stock, trigger mechanism and cavity for inserting the magazine; and the detachable ammunition magazine, which holds a plurality of ammunition to be fed into the firing chamber.
AR rifle ammunition detachable magazines were optimized to hold and feed relatively slender, pointed, rimless rifle cartridges.
The AR rifle upper receiver and detachable magazine are not inherently suitable for shotgun cartridges which are relatively bulky, blunt in shape, and have a rim at the base which projects beyond the diameter of the remainder of the shotgun cartridge.
A detachable magazine can be quickly inserted and removed from the firearm to support rapid reloading of the firearm for sporting or tactical situations. Fixed magazines do not support this capability.
There exists an opportunity to invent an autoloading AR rifle based shotgun with a detachable magazine capable of utilizing the variety of commonly available standard shotgun ammunition (shotgun cartridges), exploiting the ergonomic controls, parts commonality, operational functionality, and detachable magazine of the AR rifle.
The AR series firearms use a gas operated mechanism to support autoloading functionality. The gas operated mechanism is not suitable for a shotgun platform where a short barrel is desirable for certain tactical applications. Gas operated mechanisms, such as direct gas impingement or short stroke gas piston, require a certain minimum barrel length in order to function properly. To overcome this unsuitability, there has arisen a need for a “short-recoil” type mechanism to support the autoloading functionality. A short-recoil type mechanism does not adversely affect applications requiring shorter barrel lengths, since short-recoil action does not require certain minimum barrel lengths in order to function properly.